Mixed refrigerants are used in industry for various reasons. They may be used as a matter of convenience when a suitable process stream or streams of suitable composition is available to supply the charge and makeup requirements for the refrigeration system.
Often a mixed refrigerant is preferred since such a refrigerant may have a boiling range rather than essentially a boiling point, as is the case with a substantially pure refrigerant. A refrigerant with a boiling range has advantages when a multicomponent fluid is to be condensed to aid in distributing the condenser load and to reduce overall refrigeration power requirements.
A problem commonly encountered when mixed refrigerants are used in a closed refrigeration system is the tendency for high boiling and low boiling components to segregate in the system. Higher boiling components tend to accumulate in the evaporator, and lower boiling components tend to accumulate in the condenser. When this situation occurs, the evaporator operates at a higher temperature, reducing refrigeration capacity, and the condenser requires a higher pressure to condense refrigerant, all increasing compression power requirements and wasting energy.